Si Contact System Research Articles

Soft X-ray spectroscopy (SXS) study of electronic and atomic structures of a Ni silicide-Si system

A non-destructive analysis of a NiSi 2 (epitaxial film)-Si(111) contact system was carried out using the distinct differences of Si(L 2,3) soft X-ray emission band spectra between NiSi 2 and Si single crystals. Another comparative analysis relied on the fact that the soft X-ray production depth increased in a solid when increasing the energy of the primary electron, E p . Electronic and atomic structures of the surface together with the interface of a Si crystal with a NiSi 2 layer on top became clarified when changing E p between 0.85 and 4 keV.

Contact resistivities of Al and Ti on Si measured by a self-aligned vertical Kelvin test resistor structure

The specific contact resistivities (ρ c ) of Al(1% Si) n +− Si and TiSi 2 n +−Si contact systems were studied by using a “self-aligned” vertical Kelvin test resistor structure. The SAVTR structure can eliminate the misalignment error of the vertical test structure, thus the results obtained are closer to the true specific contact resistivities than those obtained by any other methods. For the Al(1% Si) n +− Si contact system, a specific contact resistivity of 1 × 10 −7 Ω-cm 2 has been obtained. For the TiSi 2 systems, the TiSi 2 (direct-reaction)/ n +-Si contact system offers a lower ρ c than that of the TiSi 2 (coevaporation)/ n +−Si system. For both the TiSi 2 (direct-reaction and coevaporation) contacts, the ρ c does not change even after the system is annealed as high as 900°C.

Barrier effect of e-beam evaporated tungsten interlayer in Al/W/PtSi metallization layer

The reaction characteristic of Al/PtSi and the effectiveness of W diffusion barrier interlayer in the Al/W/PtSi metallization system are examined. Ideal I-V characteristic and low constant end resistance are obtained in PtSi/n-Si and PtSi/n+Si contact system. However, Al/PtSi/n-Si and Al/PtSi/n+P Si can not stand the sintering for 30 min at 350° C and 400° C, respectively. A new phase, PtAl2, is observed after sintering at 350° C for 15 min. The W diffusion barrier layer is proved to enhance the stability of Al/PtSi. Tungsten layers of 500A and 1000A are effective up to 450° C annealing for 1 hr and 500° C for 4 hrs, respectively. A new phase, W12Al, is observed after sintering at 550° C for 15 min.

Simultaneous formation of TiN and TiSi2 by lamp annealing in NH3 ambient and its application to diffusion barriers

The dependence of TiN/TiSi2 bilayer formation on Si by lamp annealing of Ti upon annealing temperature, ambients, and impurity in Si was investigated. In NH3 ambient, nitridation ratio on undoped Si at 680 and 800 °C is 40% and 25%, respectively. When annealing is performed in N2, the nitridation ratio of Ti is only about 25% at both 680 and 800 °C. The above dependence of nitridation ratio on annealing ambient is due to the difference in decomposition energy of gas molecules. The nitridation ratio increases on arsenic-implanted Si because of a retardation effect of the arsenic on the silicidation reaction. The bilayer formation process was applied to the AlSi contact metallization on the n+ diffused layer. From measurements on electrical characteristics of the AlSi/TiN/TiSi2/n+ Si contact system, the following results were obtained: (1) Contact resisitivity is 3.5–5.3×10−7 Ω cm2. (2) The TiN/TiSi2 contact electrode is thermally stable against Al. In particular, when the bilayer is formed in NH3 at comparatively lower temperature, its thermal stability is still further improved. This is due to the formation of the thicker surface TiN layer.

Specific contact resistivity measurement by a vertical Kelvin test structure

A vertical Kelvin test structure is used to measure the specific contact resistivity of the Al (1-percent Si)/Si and Al (1-percent Si)/TiSi <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /Si contact system. For the vertical test structure, the driving current flows "vertically," thus the current crowdings and sheet resistance effects are eliminated and measurement on the true specific contact resistivity becomes possible. Experimental works show that results obtained by using this vertical structure are closer to the true specific contact resistivities than those obtained by using the conventional six-terminal Kelvin method. It is also found that R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sd</inf> , the sheet resistance directly underneath the contact pad, is much less than that of the conduction bar without the contact pad. A value of (1.17 ± 0.17) × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> Ω . cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> specific contact resistivity is obtained for the Al (1-percent Si) /TiSi <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (direct reaction) /Si system.

Thermal stability of the Al/PdxW100−x/Si contact systems

Interactions of thin films of Al and Pd-W alloys (Pd80W20 and Pd20W80) deposited on Si and on SiO2 have been studied using Auger-electron spectroscopy, Rutherford backscattering spectrometry, x-ray diffraction, and forward current-voltage measurements of Schottky-barrier height. For the bilayer films deposited on the inert substrate of SiO2, Pd reacts with Al, forming Al-rich Al-Pd intermetallic compounds at 400 °C. Furthermore, in the Pd-rich alloys (Pd80W20) Al permeates through the whole alloy film readily at 500 °C, while in the W-rich Pd20W80 the integrity of the alloy film is preserved even following annealing at 600 °C. For the bilayer films deposited on single-crystal Si, the results of annealing show extraction of Pd to both sides of the alloy, forming Pd2Si at the Si side and Al-Pd intermetallic compounds at the Al side. In the case of the Pd-rich alloy (Al/Pd80W20/Si) contact deterioration due to Al penetration to the substrate interface is observed at 500 °C and possibly at 400 °C. In the case of the W-rich alloy (Al/Pd20W80/Si) the stability of the contact is preserved even following annealing at 550 °C for 30 min; the structure after the annealing is Al-Pd/Pd-W/Pd2Si/Si. The W-rich alloy is very promising for contact applications in Si devices due to the fact that both a shallow silicide contact and a built-in diffusion barrier are simultaneously obtained.